Spatial and temporal statistics of clear-air-radar signals
As numerical models of turbulent flow in the Atmospheric Boundary Layer (ABL) improve in their temporal and spatial resolution, high-resolution remote sensing measurements become increasingly important for validation and improved understanding. The Turbulent Eddy Profiler, a recently developed UHF imaging radar, provides a tool both to observe the three dimensional structure of clear-air scattering from refractive index turbulence with fine spatial and temporal resolution and to explore the limits to this resolution. This dissertation focuses on the space-time statistics of the clear-air radar signal and their implications on measurements of winds, temperature, and spatial coherence.
A theoretical analysis of the statistics of the radar echo is presented, resulting in a general expression of the space-time autocorrelation of the radar signal. This expression is later used in the analysis of wind profiling techniques, where Spaced Antennas (SA) algorithms are compared to Doppler Beam Swinging (DBS) methods. The relation between SA and DBS methods is studied, leading to the conclusion that DBS methods are better suited for use with imaging radars where beams may be electronically steered.
The implementation of a TEP-based Radio Acoustic Sounding System (RASS) to retrieve temperature fields is described. Using TEP, the spatial structure of RASS echoes using a UHF radar is revealed for the first time. Three-dimensional RASS-measurements of virtual temperature are used to explicitly calculate structure functions, and to retrieve profiles of the structure function parameter of virtual temperature.
The stream-wise spectral coherence of the vertical wind field in the convective boundary layer is studied using TEP data. Results are compared to theoretical curves that include the effect of volume averaging inherent to radar data, and to Large Eddy Simulation data. There is scant experimental validation of these relationships. Experimental results are found to be in good agreement with both simulations and theory under convective conditions. This promising result suggests multiple beam radars may study spatial coherence under neutral or stable conditions.
0768: Environmental science